Apparatus for half tone marking electrostatic paper

Claim 2

In a facsimile recorder including a marking circuit of the type adapted to be supplied by an analogue facsimile signal and including means for providing a square wave clock signal, means for integrating the square wave clock signal to produce a triangular waveform, means providing a voltage reference, means to shift the triangular waveform in amplitude with reference to said voltage reference responsive to the magnitude of said analogue signal to produce signals of varying time duration, and means to use said signals of varying time duration to produce marking currents, whereupon the duration of the marking pulses vary in length and are centered on the altitude of the triangular waveform so that a screen effect is achieved in the marked copy, the improvement comprising means for producing a modified waveform having a non-linear shape from said triangular waveform, said non-linear shape in accordance with a desIred half tone characteristic, and means to use said modified waveform to produce said signals of varying time duration.

Claim 3

A facsimile recorder according to claim 1 in which is included means for producing spikes on said non-linear shaped waveform so as to render better tonal quality in case of misadjustment of signal level.

Claim 4

A facsimile recorder according to claim 2 in which said means for producing spikes on said modified waveform is a differentiating circuit for said square waveform.

Claim 5

A facsimile recorder according to claim 1 in which said means for producing a waveform of non-linear shape from said triangular waveform is an amplitude shaper.

Claim 6

A facsimile recorder according to claim 4 in which said amplitude shaper is a pair of opposed diodes connected in parallel with a resistor network.

Claim 7

A facsimile recorder according to claim 1 in which said means to shift said modified triangular waveform is an operational amplifier.

Claim 8

A facsimile recorder according to claim 1 in which said means to use said signals of varying time duration to produce marking pulses incorporates the base to emitter circuit of a transistor.

Claim 9

In a facsimile recorder including a marking circuit of the type adapted to be supplied by an analogue facsimile signal and including means for providing a square wave clock signal, means for integrating the square wave clock signal to produce a triangular waveform, means providing a voltage reference, means to shift the triangular waveform in amplitude with reference to said voltage reference responsive to the magnitude of said analogue signal to produce signals of varying time duration, and means to use said signals of varying time duration to produce marking currents, whereupon the duration of the marking pulses vary in length and are centered on the altitude of the triangular waveform so that a screen effect is achieved in the marked copy, the improvement comprising means for producing a modified waveform having a non-linear shape from said triangular waveform, said non-linear shape in accordance with a desired half tone characteristic, the rise time of the leading edge of said modified triangular waveform steeper both at the base and apex thereof and flatter at its intermediate portion as compared to the linear rise time of the unmodified triangular waveform, and means to use said modified waveform to produce said signals of varying time duration.

Claim 10

In a facsimile recorder including a marking circuit of the type adapted to be supplied by an analogue facsimile signal and including means for providing a square wave clock signal, means for integrating the square wave clock signal to produce a triangular waveform, means providing a voltage reference, means to shift the triangular waveform in amplitude with reference to said voltage reference responsive to the magnitude of said analogue signal to produce signals of varying time duration, and means to use said signals of varying time duration to produce marking currents, whereupon the duration of the marking pulses vary in length and are centered on the altitude of the triangular waveform so that a screen effect is achieved in the marked copy, the improvement comprising means for producing a modified waveform having a non-linear shape from said triangular waveform, said non-linear shape in accordance with a desired half tone characteristic, the rise time of the leading edge of said modified triangular waveform steeper both at the base and apex thereof and flatter at its intermediate portion as compared to the linear rise time of the unmodified triangular waveform, and means to use said modified waveform to produce said signals of varying time duration.